I. Field of the Invention
The present invention relates to a pulse latching solenoid which maintains a latched position after termination of the latching pulse.
II. Background Information
Solenoids which latch into position upon receipt of an activation pulse and maintain that position upon termination of that pulse are known. One such solenoid is, for example, disclosed in U.S. Pat. No. 4,004,258 issued to Arnold. The Arnold-type solenoid has a plunger of paramagnetic material located between two stops of similar material. Fixed permanent magnets which impart a flux to the moveable plunger cause the plunger to adhere to the stop to which the plunger is moved. Movement of the plunger is accomplished by a respective winding adjacent each stop which, when excited by an external electrical pulse, momentarily exerts an attractive force on the plunger, causing the plunger to move toward the corresponding stop. When moved toward a stop, a gap is closed between the plunger and that corresponding stop, thereby holding the plunger in position after termination of the activating pulse.
The Arnold patent further discloses use of a reed switch to sense momentary flux generated by the exciting wire at a leakage gap near one of the stops to thereby indicate plunger position.
The type solenoid disclosed in Arnold does not exhibit a fail safe characteristic. That is to say, if the Arnold-type solenoid is vibrated causing the plunger to move from one stop to the other, the plunger will latch in either stop. Accordingly, in the presence of vibration, there is no assurance that the plunger disclosed in Arnold will always come back to rest in a fail safe position.
In addition, since Arnold discloses the utilization of a plurality of permanent magnets, both of the Arnold coils must be of sufficient size to overcome the effects of these permanent magnets. This requirement limits the degree to which an Arnold-type solenoid may be miniaturized.
It is, therefore, an object of the present invention to provide a latching solenoid which returns automatically to a fail safe position when exposed to vibration.
Another object of the subject invention is to provide a latching solenoid of minimal size and power consumption.
A still further object of the subject invention is to provide a latching solenoid with a simple external position indicator.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention.